1. Technical Field of the Invention
This invention relates to a method for manufacturing a portion of a valve and assembling the valve. More particularly, this invention relates to a method for manufacturing the guide base of a full-open valve and attaching the guide base to an upper valve body of the valve.
2. Description of the Prior Art
In oilfield drilling and well servicing operations it is frequently necessary to introduce large quantities of drilling mud and other fluids into the drilling or producing string to promote the drill operations or to stimulate the producing formation. To accomplish this, large surface pumps are used which must be capable of pumping up to 200 gallons per minute at pressures in excess of 15,000 psi. Such pumps include one or more valves which control the flow of the drilling mud or other fluids being injected from surface storage vessels, through the pump into the string or completion tubing. Normally, such valves are either in a full-open or a full-closed position. Because of the large quantities of fluids which must pass by the valve when in an open position, it is important that the valve have a structure which minimizes the interference with fluids flowing past. This is determined by that portion of the valve which holds the valve head or the upper valve body in place (referred to herein also as the guide base) and permits smooth vertical movement of the upper valve body from a closed to an open position and vice versa.
Prior art valves include the Harrisburg Imperial valve and seat as shown at page 4115 of the 1982-83 Composite Catalog for Oil Field Equipment and Services, published by World Oil, and the Harrisburg Roughneck.TM. valve and seat available through Harrisburg, Inc. of Houston, Tex. and shown on page 5 of Harrisburg's 1986-87 General Product Catalog and FIGS. 1a and 1b hereto.
The Imperial valve attempts to maximize fluid flow by using a single shaft attached to the upper valve body. However, to keep the valve vertical, this design requires a series of cross-arms located within the seating cylinder which extend horizontally from the walls of the seating cylinder inwardly to a ring member. The shaft of the valve is inserted into the ring member and is thereby restrained horizontally. However, due to available materials, the cross-arms and the ring member are usually of a minimum size which restricts up to one-third of the cross-sectional area of the seating cylinder through which the fluids must flow. Historically, Imperial valves were used in mud pumps in drilling operations.
In an attempt to improve on the flow interference characteristics of the Imperial valve in fracturing operations, the guide base was modified to include four leg members adapted to engage the walls of the seating cylinder. The leg members permit vertical movement of the valve but prevent a cocking movement which might otherwise jam the valve within the seating cylinder. For example, see the TRW Mission Service Master.RTM. valve at page 7833 of the 1982-83 Composite Catalog for Oil Field Equipment and Services. It was found that such a guide base configuration is preferred because it provided a minimal amount of interference with fluid flow while still providing sufficient horizontal and vertical support to the upper valve body. However, such guide bases were manufactured using the forging process which has many inherent manufacturing disadvantages. In an attempt to improve on the performance of such a design, Harrisburg offers the Roughneck.TM. valve.
In the manufacture of the Roughneck.TM. valve, the upper valve body is forged while the guide base is made by the investment casting process (also known the "lost-wax" process), well known to those skilled-in-the-art. Very briefly, the investment casting process as it applies to the Roughneck.TM. valve is as follows. Model guide bases are made from wax using an injected pattern mold. Several of the wax guide bases are then assembled in a cluster or "tree" arrangement and dipped into a ceramic slurry. The slurry may be a paste comprising a fine-grained refractory mold material and a bonding agent so that the wax mold becomes coated with this mixture. The ceramic mold is then fired in a furnace causing the wax models to melt. The result is a casting mold made of ceramic. The desired final material is then selected and poured into the mold. The mold is then broken and the individual guide assemblies removed and prepared for attachment to the forged upper valve bodies. Each guide base is attached to an upper valve body using inertia friction welding, a technique well known to those skilled-in-the-art.
The investment casting process, however, is expensive and time-consuming. There is a need, therefore, for an inexpensive method of manufacturing the guide base and attaching it to the upper valve body.